Field of the Invention
The invention relates in general to the field of tribology.
Description of the Prior Art
The field of tribology involves the study of friction and wear on materials. Two or more objects are brought into contact with each other and a relative motion is started between the two contacting materials for the purpose of measuring the resulting friction forces. Over time a “wear” track may be created as result of damage caused by the two materials rubbing against each other; therefore, the wear on one or both of the objects can also be measured.
There are many different configurations of mechanical testers, each performing a specific dedicated test. The present invention describes a unique piece of equipment that allows the user to perform multiple tests with multiple configurations with a single mechanical tester and interchangeable, modular sample stages and accessories.
The conventional equipment used for measuring friction and wear is dedicated to a particular test type and a corresponding test configuration. Examples include, without limitation, the configurations referred to in the art as block-on-ring, pin/ball/disk-on-disk, and reciprocating pin/ball on flat. The first represents a configuration where the sample stage includes a horizontal drive shaft rotating around its main axis. A ring specimen is coupled to the shaft for concurrent rotation and a test block is pushed radially against the edge of the ring with a known force. The friction force and/or the torque imparted on the shaft are measured, from which the coefficient of friction between the block and the specimen material can be calculated based on the known load (i.e., the normal force applied by the block).
Similarly, for the ball-on-disk, pin-on-disk or disk-on-disk test configurations, a disk specimen is mounted horizontally on a vertical rotating shaft in the sample stage. A ball or pin specimen is brought down from above into contact with the spinning face of the disk at a known radial distance from the axis of the shaft and a known normal force is applied. Thus, the frictional force between the ball or pin and the spinning disk and the resulting wear can be measured. Alternatively, a fixed disk, rather than a ball or pin, is aligned axially with the spinning disk coupled to the stage and the two are brought into contact with a known force. In this configuration the friction and wear between the two disks can similarly be measured.
The third exemplary type of test equipment is a reciprocating-type tester. In this configuration an eccentric crank arm is used to transfer the rotary motion of a vertical drive shaft to a reciprocating motion in a horizontal plane of the stage where the sample is mounted. By applying a constant rotational motion to the drive shaft, the horizontal reciprocating motion follows a sinusoidal velocity profile. A test specimen (a flat sample) is mounted on the reciprocating plane and again a ball or pin specimen is brought into contact with a known normal force. The resulting frictional force is measured and the coefficient can be calculated. Wear tests can be similarly carried out in conventional manner.
Each of these tests is normally carried out on a different, dedicated test machine. Therefore, multiple machines are required, which can be inefficient and therefore undesirable if all available machines are not used simultaneously. The capability of carrying out multiple testing requires a lot of laboratory space, which is typically the most expensive space in a production setting. It is also inefficient and expensive due to the fact that many of the same components, such as computers, controllers and sensors, are necessarily provided as duplicates for each dedicated testing unit.
U.S. Pat. No. 6,418,776 describes a universal tester wherein alternative modules, each containing a motor and a dedicated drive, are available for use in different test configurations, such as described above. Each module includes a self-contained drive with a motor and is attached to a base plate in the frame of the unit. While this type of system requires less laboratory space and can be more economical than multiple dedicated testers, each replaceable stage unit still has its own motor, which is often the single most expensive component of the replaceable module. Also, because the motor is included in each modular stage, each module is necessarily larger than desirable in relation to the space available inside the base of the instrument and therefore only relatively small motors can be used. In addition, the presence of these motors in the stage module limits the access to the sample area because of the space occupied by them and by the cables needed to supply power to the motor, all of which limits the space available for specimens attached to the carriage of the tester and for specimens mounted on the modular stage.
A universal tester of this type is also difficult for the user to configure and use properly with the software. In what has turned out to be a major problem and concern in the industry, the software must be set-up manually for each test configuration or there must be a dedicated piece of software for each test type, which can be cumbersome for the user and lead to serious mistakes when a test is not properly set up. The wrong choice of test parameters will produce misleading results; more importantly, however, it can also create dangerous situations due to unwarranted mechanical stresses that can result from erroneous test programming. If different test programs (referred to in the art as “scripts”) are provided by the developer for each machine, they also require continuous technical support, which adds cost for the user as well as the supplier. This invention is directed at solving these problems with a mechanical tester capable of performing measurements in all above-described configurations with a single rotary drive.